Abstract: DESCRIPTION: (adapted from the application): This proposal describes genetic and demographic experiments with laboratory populations of Drosophila. There are four specific aims: (1) To estimate population heterogeneity for frailty, using multi-level stress experiments; (2) To test for "physiological plateaus" by collecting longitudinal data on metabolic rate, reproductive behavior, fertility, and 1ocomotor activity; (3) To test the pleiotropy hypothesis by QTL-mapping in recombinant inbred (RI) lines; (4) To test a specific genetic model of genotype x enviroment interaction by repeating the QTL-mapping in multiple environments. The proposed experiments address basic questions: Why do mortality curves decelerate at advanced ages? What are the biological correlates of altered mortality dynamics? Are the genes that extend life span pleiotropic? Do different genes cause variation in life span in different environments? Notable features of the proposed experiments are: (1) large sample sizes are used; (2) there is an emphasis on mortality dynamics; (3) the approach integrates demographic and biological methods; (4) the investigators will use recently constructed KI lines, which are an unusually valuable resource for QTL-mapping and pleiotropy tests; (5) heterogeneity for frailty has not previously been directly measured in any experimental population.